Synchronizing optical scan and electrical addressing of a single-panel, scrolling color LCD system

• US 20030231159A1
• Filed: 06/17/2002
• Published: 12/18/2003
• Est. Priority Date: 06/17/2002
• Status: Active Grant

• Current Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Original Assignee: Koninklijke Philips Electronics N.V. (Koninklijke Philips N.V.)
• Inventors: Dalal, Sandeep M.
• Granted Patent: US 6,950,088 B2
• Time in Patent Office: Days
• US Class Current: 345/102
• CPC Class Codes: G09G 2310/0235 Field-sequential colour display
• CPC Class Codes: G09G 2310/024 Scrolling of light from the illumination source over the display in combination with the scanning of the display screen
• CPC Class Codes: G09G 2310/08 Details of timing specific for flat panels, other than clock recovery
• CPC Class Codes: G09G 2360/145 the light originating from the display screen
• CPC Class Codes: G09G 3/342 using several illumination sources separately controlled corresponding to different display panel areas, e.g. along one dimension such as lines
• CPC Class Codes: H04N 9/3117 by using a sequential colour filter producing two or more colours simultaneously, e.g. by creating scrolling colour bands

Abstract

The electrical scan which applies data for one of the red, green and blue colors of a liquid crystal display (LCD) to the pixels of each row of the display and the optical scan of the panel with the color stripe of that color are synchronized to ensure sufficient time for the switching of the pixel from one color value to another. Synchronizing the electrical and optical scans creates a better color rendition of the displayed image without any inter-color mixing artifacts. Arrays or groups of photosensors are positioned laterally adjacent the active portion of the panel and each array is covered by a filter which passes light of only one of the three colors (red, green and blue) used in the display. The color stripes providing the optical scan are scrolled simultaneously over both the active portion of the panel and the arrays of sensors, with the electrical signals from the sensors providing an indication of the positions of the leading and trailing edges of each color stripe at each instant, and thus the instantaneous velocity of each stripe. The signals from the sensors are provided to a control circuit which determines the order in which the rows of pixels are addressed and for which of the colors to provide data in each addressed location in order to maintain the critical switching time in spite of variations in relative velocities of the three color stripes.

Claims

1. The method of driving single-panel, scrolling, color liquid crystal displays comprising an array of pixels arranged in a plurality of rows, wherein stripes of a plurality of different colors are consecutively scrolled in a predetermined direction across the surface of said panel with the trailing and leading edges of successive stripes in spaced relation to provide an optical scan, the leading edge of each of said stripes being preceded by an electrical addressing scan representing an addressing of discrete locations on said panel with the data for the following one of said colors, said method comprising:

a) providing electrical signals commensurate with a continuous indication of the location on said panel of the leading and trailing edges of each of said stripes which are present on said panel; and

b) generating said electrical addressing scan at a time preceding by a predetermined interval said leading edge of said following color stripe, said predetermined interval being sufficient to allow full switching time of the individual pixels of said display from one color value to another.

2. The method of claim 1 wherein said electrical signals are generated by photosensors.

3. The method of claim 2 wherein said photosensors are arranged in a number of groups corresponding to the number of said plurality of different colors, each of said groups being responsive to a respective one of said colors.

4. The method of claim 3 wherein said panel is divided into a first portion comprising said pixels and forming an active display, and a second portion comprising said groups of photosensors.

5. The method of claim 4 wherein said panel is made in a standard silicon CMOS process with both said pixels and said photosensors integrated on said panel.

6. The method of driving a single-panel, color LCD to improve color rendition of the displayed image without inter-color mixing artifacts comprising:

synchronizing electrical addressing of the rows of pixels making up said panel with data for a predetermined color with the optical scan of said panel with a light stripe of said predetermined color, thereby providing a predetermined time delay between said electrical addressing and said optical scan for each of said rows.

7. The method of claim 6 wherein said synchronizing includes continuous monitoring of at least one of the velocity and position of said light stripe for each of said colors.

8. The method of claim 7 wherein said velocity and/or position monitoring is implemented by photosensors which are traversed by said optical scan with said light stripes.

9. The method of claim 7 wherein said synchronizing further includes controlling the sequence of location and color data of said electrical addressing in response to said light stripe velocity.

10. The method of claim 7 wherein said predetermined time delay is established at no less than the minimum critical switching time of said pixels from one color value to another.

11. Apparatus for controlling the timing of electrical addressing signals provided to the rows of pixels in a LCD panel relative to successive optical scans by light stripes of a plurality of different colors which are scrolled across the surface of said panel, said apparatus comprising:

a) a plurality of groups of photosensors corresponding in number to said plurality of different colors, each of said groups generating electrical signals in response to impingement thereon of a corresponding one of said colors, said groups being positioned to receive said optical scans as the latter are scrolled across said panel, whereby said electrical signals are indicative of at least one of the velocity and position of said optical scans;

b) a control circuit to which said electrical signals are provided as input signals, said control circuit generating control signals commensurate with the velocities and/or positions of each of said optical scans as indicated by said input signals;

c) an addressing circuit adapted to generate electrical scans each directed to a particular one of said rows with color data for one of said colors in response to said control signals, the order of addressing said rows and the selection of the color for which data is provided being selected by said control circuit to maintain a critical switching time between said electrical scan providing color data for one of said colors and the optical scan for that color, said switching time being sufficient for said pixels to change from one color value to another.

12. The apparatus of claim 11 wherein each of said groups of photosensors is covered by a filter which passes only light of one of said plurality of colors.

13. The apparatus of claim 12 wherein said photosensors are integrated on the surface of said LCD panel.

14. The apparatus of claim 13 wherein the number of said plurality of colors is three, namely, red, green and blue.

15. The apparatus of claim 14 wherein said groups of photosensors are arranged in side-by-side relation in strips extending along one or both side edges of said panel.

16. A color LCD panel comprising:

a) an active portion comprising a plurality of horizontal rows of individual pixels, each responsive to an electrical scan carrying data for one of a plurality of colors and an optical scan which is scrolled in a vertical direction over said rows of pixels; and

b) a sensing portion comprising a plurality of arrays of photosensors, corresponding in number to said plurality of colors, positioned laterally adjacent one side of said active portion to receive said optical scan simultaneously with said active portion, and to produce an electrical signal in response to impingement thereon of said optical scan.

17. The LCD panel of claim 16 wherein the number of said plurality of colors and of arrays is three.

18. The LCD panel of claim 17 and further including three color filters, one positioned in covering relation to each of said arrays, each of said filters passing light of a respective one of said colors.

19. The LCD panel of claim 18 wherein said pixels and photosensors are integrated on said panel, the latter being made in a standard CMOS process technology.